International patent application publication WO 2008083093 describes a chip that detects wake-up events. A power management circuitry selectively provides power to a processor and to a I/O wake-up logic circuitry. The wake-up logic circuitry detects and responds to the wake-up events while power is provided by the I/O power supply. Multiple of such devices may be coupled in a daisy chain, each device having a wake-up network output to be coupled to a wake-up network input of a next device in the chain. The first device is coupled to a chain controller via the wake-up network input, and the last device in the chain may loop-back via its wake-up network output to a loopback input on a chain controller.
A drawback of the device disclosed in this prior art publication is that a daisy chain requires said loopback to verify whether the last device has actually detected said wake-up. Also it cannot be verified whether intermediate devices in the daisy chain have actually responded to the detected wake-up until communication from the chain controller device is again established.